Sharing the same exact structure across two instances of odrive (your Windows desktop and your Mac, for example), is not something we recommend or test. The main issue is that one odrive may see new placeholder files that are “foreign” to it, since they were created by the other instance. odrive should be able to deal with this, replace them with its own, and continue on but, again, its not something we can test or support.
Similarly, I wanted to reiterate that we also don’t test or support placing the whole odrive folder on a external drive, as stated here: https://docs.odrive.com/docs#section--move-odrive-folder-to-another-volume-. It is something that may work, but can possibly cause some complications. For example, it can create issues with reflection/pick-up of changes, permissions, CPU heat, disk churn, inaccurate scans, user feedback lag, and other problems.
Our “sync to odrive” feature allows you to sync specific areas on external volumes without needing to move the entire odrive folder to an external volume. Have you tried that feature yet? https://www.odrive.com/usageguide#syncexternalfolders
For the timestamp issues, if you are able to adjust the time on these files that were made back in the 70’s ;), I expect it to clear up the problem you are having.
For your trash, having the placeholder and “real” file alongside each other is not a problem (the “real files” just takes the place of the placeholder and the placeholder is removed), so there is no need to remove placeholders.
Currently there isn’t a way to perform a mass trash recovery, bu if you recover a folder in the trash that contains a bunch of trashed files, it will recover the files within it, automatically.
Additionally, you can simulate a mass recovery if you unsync the parent folder of the items in the trash. Unsync of a folder will discard any pending deletes inside, which will remove them from the trash. Re-syncing that folder will show you the files/folders again.